1. Field of the Invention
The present invention relates to a bi-directional optical transceiver module with double caps. More particularly, the present invention relates to a bi-directional optical transceiver module having double caps in which elements, such as a semiconductor laser and a photodiode, are integrated.
2. Description of the Related Art
Referring to FIG. 1 showing the construction of a conventional bi-directional optical transceiver module, the conventional bi-directional optical transceiver module includes an optical waveguide element 132, a sleeve 131, a lens holder 120 serving as a body tube and having a cylindrical construction, a lens 140 converging each of input and output optical signals, a stem 114 supporting a lower end of the lens holder 120, and a cap 110 disposed on the stem 114.
The optical waveguide element 132 is packaged in the sleeve 131. The optical waveguide element 132 serves as a medium through which an input optical signal 160 or an output optical signal 170 is transmitted when they are inputted into or outputted from the bi-directional optical transceiver module, respectively.
The lens holder 120 has a cylindrical construction, supports the lens 140, and serves as a body tube forming a passage for the input optical signal 160 and the output optical signal 170. The optical waveguide element 132 is inserted and fixed in an upper end of the lens holder 120.
The lens 140 is an element for converging the input optical signal 160 inward of the cap 110 and the output optical signal 170 toward the inserted end of the optical waveguide element 132 and is packaged in an upper portion of the lens holder 120. In general, the input optical signal 160 and the output optical signal 170 have different wavelengths than each other.
Referring to FIG. 2, the cap 110 is assembled with and covered on the upper surface of the stem 114. The cap 110 has a hole formed through a central portion thereof, so that the input and output optical signals can be transmitted and received through the hole. Further, a view window 117 is disposed just under the hole. The view window 117 prevents foreign material from coming into the cap 110 while allowing the input and output optical signals to pass through the view window 117.
The contents of the cap 110 include optical elements such as a photodiode 112, a semiconductor laser 113, and a wavelength division multiplexing filter 115. The photodiode 112 receives the input optical signal 160 and converts it to a corresponding electrical signal. The semiconductor laser 113 modulates the electrical signal into the output optical signal 170. The wavelength division multiplexing filter 115 separates the input optical signal 160 and the output optical signal 170 from each other and transmits them through their own respective paths.
The stem 114 is formed in a plurality of holes (not shown) passing through both faces, and a plurality of the metal lead wires 150 of the hole are arrayed to protrude its portion on the upper face of the stem 114. The holes which the metal lead wires 150 are arrayed are filled with a sealing material (not shown) for fixing the metal lead wires 150. The metal lead wires 150 comprises a direct current (DC bias lead), a high-frequency lead connected to a cathode of the semiconductor laser 113, an anode lead connected to an anode of the photodiode 112 for monitoring an optical element outputted from the semiconductor laser 113, and a common lead connected to a cathode of the semiconductor laser 113 and the photodiode 112.
The photodiode 112 is created for monitoring the optical element outputted from the semiconductor laser 113 on the stem 114, and each of the semiconductor laser 113 and the photodiode 112 is electrically connected to metal lead wires 180 by each of the leads 150 and a wire bonding method.
The stem 114 serves as a substrate for the optical elements housed in the cap 110 and supports the lower end of the lens holder 120.
The advantage of a conventional bi-directional optical transceiver module is that it allows the packaging of a semiconductor laser and a photodiode together in a cap, thereby giving the conventional bi-directional optical transceiver module a relatively small volume where it may be employed in a relatively small optical system.
However, in the conventional bi-directional optical transceiver module, much time is required in assembling the wavelength division multiplexing filter, since the wavelength division multiplexing filter must be mounted at a predetermined angle in the optical path of the input and output optical signals. Further, when a portion of scattered or diffusion-reflected light generated in the wavelength division multiplexing filter, view window, or other elements in the path of the optical signals are introduced into the photodiode, they are superimposed on the normal input optical signal causing optical crosstalk. In addition, the electromagnetic waves generated by the lead wires of the semiconductor laser may also be introduced into the photodiode causing further interference with the electrical signal created in the photodiode.